Organofunctional silanes are known in the art as coupling agents, adhesion promoters, and surface modifiers. For example, silicate esters, typically alkoxysilanes, such as methacryloxypropyltrimethoxysilane, octyltriethoxysilane, and/or tetraethoxysilane, are used in the preparation of ceramic coatings and binders to improve adhesion, and for surface modification. In most commercial silane surface treatment applications, the alkoxy groups of alkoxysilanes are hydrolyzed to form silanol-containing species, which are highly reactive intermediates responsible for bond formation with a substrate. Hydrolysis of the alkoxy groups may occur during the formal preparation of aqueous silane solutions or by the reaction of the silane with adsorbed moisture on substrate surfaces. A general overview of the reaction and bonding mechanism of alkoxysilanes may be found, for example, in Arkles, B. et al., Factors Contributing to the Stability of Alkoxysilanes in Aqueous Solution, Silanes and Other Coupling Agents, pp. 91-104, ed. K. Mittal (1992).
In aqueous environments, most silanols used in surface treatment applications are unstable in their monomeric form. Once hydrolysis is initiated, these silanols may condense relatively quickly within hours with other silanols and their alkoxy precursors, forming gels or precipitates which have no utility for surface modification. Trialkoxysilanes are known to be more stable sources for silanols, but have numerous disadvantages, including production of hydrolysis by-products that are undesirably toxic and/or flammable, and difficult to remove from solution.
Several methods have been employed in the prior art to stabilize silane solutions. For example, one approach has been to cohydrolyze a hydrophilic silane with a surface modifying silane, forming silanol-rich oligomeric condensates. These silanes maintain greater silanol stability in solution and exhibit substantially greater wet bond strength relative to conventional silanes.
Thus, there is a great need in the art for an organofunctional silane that is useful on surface application modifications, would facilitate the hydrolysis of the other silanes in solution and be more effective in stabilizing the reactive species while in solution.